A series of iron(II) bis(triflate) complexes [Fe(L)(OTf)2] contg. linear tetradentate bis(pyridylmethyl)diamine ligands with a range of ligand backbones has been prepd. The backbone of the ligand series has been varied from a two-carbon linkage [ethylene (1), 4,5-dichlorophenylene (2) and cyclohexyl (3)] to a three-carbon [propyl (4)) and a four-carbon linkage (Bu (5)]. The coordination geometries of these complexes have been investigated in the solid state by X-ray crystallog. and in soln. by 1H and 19F NMR spectroscopy. Due to the labile nature of high-spin iron(II) complexes in soln., dynamic equil. of complexes with different coordination geometries (cis-α, cis-β and trans) are obsd. with ligands 2-5. In these cases, the geometry obsd. in the solid state does not necessarily represent the only or even the major geometry present in soln. The ligand field strength in the various complexes has been investigated by variable temp. magnetic moment measurements and UV-vis spectroscopy. The strongest ligand field is obsd. with the most rigid ligands 1 and 2, which generate complexes [Fe(L)(OTf)2] with a cis-α coordination geometry and the corresponding complexes [Fe(L)(CH3CN)2]2+ display spin crossover behavior. The catalytic properties of the complexes for the oxidn. of cyclohexane, using hydrogen peroxide as the oxidant, have been investigated. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst in the oxidizing environment. [on SciFinder(R)]